Sound waves may give clues

SPACE CENTER, Houston -- Recordings made by instruments sensitive to sound below the threshold of human hearing may help investigators build a timeline of any uncharacteristic movements made by Columbia minutes before it broke apart, scientists say.

The instruments also captured an explosion high over Texas that one scientist said could have been Columbia's cabin rupturing.

As parts of the shuttle began to break off as it streaked across the West, the spacecraft's flight behavior would have changed. Those changes would have generated distinctly different patterns of sound waves compared to previous flights.

The patterns, recorded on the ground by instruments in Texas, Nevada and elsewhere in the West, are now being examined as part of the Columbia disaster investigation.